Brake for electric motors.



No 770,028. PATENTED SEPT. 13, 1904.

L. A. TIRRILL.

BRAKE FOR ELECTRIC MOTORS. APPLICATION FILED FEB. 16, 1904.

N0 MODEL.

WITNESSES: lNvENToR,

LEONARD A. Tl RRILL...

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UNTTED STATES Patented September 13, 1904.

PATENT EEicE.

LEONARD A. TIRRILL, OF LYNN, MASSACHUSETTS, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

BRAKE FOR ELECTRIC MOTORS.

SPECIFICATION forming part of Letters Patent N0. 770,028, dated September 13, 1904.

Application filed February 16, 1904. Serial No. 193,836. (No model.)

To on whom it may concern:

Be it known that I, LEONARD A. TIRRILL, a citizen of the United States, residing atLynn, in the county of Essex and State of Massachusetts, have invented certain new and useful Improvements in Brakes for Electric Motors, of which the following is a specification.

My invention relates to electric motor drives; and its object is to provide a more efiicient means for braking than has been obtained in arrangements heretofore used.

When certain machinessuch as printingpresses, for instanceare driven by electric motors, it has been found that more satisfactory operation is obtained when the motor is belted to the driven member than when the motor is rigidly connected, as by means of gears. The flexibility obtained by. the use of a belt is an advantage in driving such machines. In operation it is frequently necessary to stop printing-presses and similar machines very quickly. A method of braking which has been commonly employed consists in short circuiting the motor-armature. This makes a very effective brake; but the strain on the belt due to the sudden stopping of the motor and the inertia of the driven member is so great that the belt is frequently damaged. By my invention I provide a strong braking action without imposing any undue strains upon the belt.

In the accompanying drawings, Figure 1 shows diagrammatically an arrangement embodying my invention. Fig. 2 is a diagram illustrating the control-circuits for the motor.

In Fig 1, M represents a motor connected, through the belt B, to the driven pulley A, mounted on the shaft a of the driven machine. O represents a magnetic brake adapted to act upon the rim of the pulley or fly wheel A. The brake O has a movable member D, which is normally held in the position shown out of engagement with fly-wheel A by gravity and by the spring 8. The movable member D carries the magnet-coil c, which when energized causes the movable member D to rise into engagement with the rim of fly-wheel A. Member D is faced with a strip of leather or other suitable material E, which serves to maintain 5 an air-gap in the magnetic circuit and which thus prevents member D from seizing the flywheel and which at the same time increases the coefficient of the friction.

In Fig. 2 I have shown the electrical con- ;5 nections of the motor and of the magnetic brake. In this figure, m represents the armature, and f the field, of motor M. c represents the winding of the magnetic brake. R representsa starting resistance for the motor. 6 H represents a controlling-switch through which the motor is connected to the source of supply 1 2. Controlling-switch H consists of the stationary contacts h to it and two sets of movable contacts g to 9 r to g. The 5 first set corresponds to the running position of the controller (indicated by '1') and the second set to the braking position of the controller, (indicated by b.) When the movable contacts are moved toward the left, so that 7 the stationary contacts engage the movable contacts g to don the first dotted line, the circuits are as follows: from line-wire 1, contact 7L2, contact 9 contact contact a to field f, contact l1, contact 9*, contact g, contact 72/, 7 5

linewire 2. The field is thus closed across the line. The second circuit is formed as follows: line-wire 1, contact 7L contact 1 con tact g contact it, through motor-armature m, through the resistance R, contact 72,, contact 30 g, contact g contact g,contact 7b line-wire 2. Thus the circuit of the armature is also closed through the resistance B. As the movable contact of switch H is moved farther to the left the resistance R is gradually cut out until 8 5 the full running position is reached. The arrangement of contacts as thus far described is the ordinary arrangement for starting a shunt-motor. Now if it is desired to stop the driven member quickly controlling-switch H 9 is thrown over to the braking position. The field-circuit is not changed. Starting from the left-hand armature-brush, the armaturecircuit is as follows: through resistance R to contact if, contact g, contact 9, contact 7& 95 through brake-coil 0, contact [L9, contact g, contact 5 contact if, to the right-hand armatu rebrush. The motor is thus short circuited through resistance R and the braking-magnet 0. Thus the motor itself is braked by the current flowing through its short-circuited armature, and at the same time a brake is applied to the fly-Wheel A by the Winding of the magnetic brake 0. Thus both driving and driven members are simultaneously braked. If the Winding of the magnetic brake is properly proportioned,practically all strain may be eliminated from the belt, and consequently all danger of breaking or stretching the belt is removed.

Although I have shown an ordinary shuntrnotor and a special form of magnetic brake, it Willbe understood that my invention is not limited to these particular forms of apparatus.

What I claim as new, and desire to secure by Letters Patent of the United States, is In combination, an electric motor, a driven member belted thereto, an electric brake for said driven member, and means for short-circui-ting the armature of said motor through the Winding of said brake, said brake being so proportioned relative to said motor that the current in the short circuit produces a braking effect on said motor and on said driven member approximately proportional to their inertia.

In Witness whereof I have hereunto set my hand this 3d day of February, 1904:.

LEONARD A. TIRRILL. Witnesses:

DUGALD MoK. MoKILLoP, JOHN A. MCMANUS. 

